The role of parent–offspring interactions during and after fledging in the Black-legged Kittiwake

Most bird species endure a high mortality at fledging, and selection should favour parental behaviour diminishing these costs. Post-fledging parental care varies greatly among species and is often linked to parent–offspring recognition. In the Black-legged Kittiwake (Rissa tridactyla), fledglings need to return to the natal nest to be fed by their parents until independence. Rejections of fledglings by non-parent adults may be fairly violent, and parents are expected to recognize and help their chicks at the time of first return. However, previous cross-fostering experiments pointed out that parents are not able to recognize their chicks up to 15 days before fledging. In this paper, we study the behaviour of both parents and juveniles at fledging. We found that parents answered significantly more to their fledgling's calls than to those of others. Compared to silent juveniles, juveniles that called before landing were more likely to be accepted by their parents. No such pattern was observed with foreign juveniles, indicating that fledglings’ voice may carry individual identity. Furthermore, fledglings found their way back to the natal nest faster when parents attended the natal nest and reacted to their offspring's calls than when they were absent or inactive. Such interactions may therefore diminish juvenile mortality at fledging.     

Brood provisioning rates and fledgling behavior of Cordilleran Flycatchers in southwestern Colorado

The behavior of young songbirds after fledging is one of the least understood phases of the breeding cycle, although parental provisioning rates and movement of fledglings are key to understanding life history evolution. We studied Cordilleran Flycatchers (Empidonax occidentalis) at two sites in southwestern Colorado, USA, from 2012 to 2017. We banded and sexed breeding adults to determine the relative contributions of males and females to nestling and fledgling care, and attached radio‐transmitters to nestlings to facilitate observations of brood behavior after fledging. Females made 60% and 78% of total observed feedings of nestlings and fledglings, respectively. Parental provisioning rates increased with nestling age, and per‐nestling provisioning rates increased with brood size. Parental provisioning rates declined just before fledging, then increased just after fledging. Fledging times of individuals in broods were asynchronous and concentrated during the late afternoon and early evening. Males stopped caring for fledglings before females even though this species is single‐brooded, with some late‐season broods being abandoned by males. Broods spent the first three weeks after fledging within 400 m of nests, after which they began to disperse. Most aspects of the breeding biology of Cordilleran Flycatchers in our study, including the duration of nestling and fledging periods, female‐dominated provisioning, and movement patterns of fledglings, were similar to those of other Empidonax species. However, the times when young fledged were not concentrated in the morning as reported in most other songbirds, and this result warrants additional study of the timing of fledging in ecologically and taxonomically similar species. The increased per‐nestling provisioning rate with increasing brood size was unexpected, and additional study is needed to determine if this increase results from a trade‐off between adult annual survival and productivity favoring increased provisioning of young in larger broods, or from the existence of high‐quality individuals where larger clutches and higher provisioning rates are linked.     

Brood division and transition to independence in Blackbirds Turdus merula

Blackbirds Turdus merula rearing young in the Botanic Garden, Oxford, were observed over three summers (1979–81). Between 0 and 10 days after fledging the young were divided between the parents so that each fed only certain fledglings and refused to feed others. This division was temporally stable. In broods where another nesting attempt followed, the male usually took responsibility for all the young, but in final broods they were divided fairly evenly. The probability of a fledgling surviving to independence declined as the number of young a parent fed increased; thus division should be favoured. However, if the female fed some young the inter-nest interval increased and the potential number of young that could be raised in that season was curtailed. This trade-off is examined by means of a model. After fledging the young improved in their ability to capture prey successfully and increased the size of the prey taken. At 15–24 days after fledging, self-feeding became more profitable than parental feeding and the young became fully independent. The timing of this transition is influenced by the parents, and it is suggested that by dividing the brood, parental feeding can be more carefully regulated so that finer control over the timing of independence is achieved.     

Recognition of Young in A Colonially Nesting Bird

Parents ought to restrict costly parental care to their genetic offspring and, particularly when the risk of misdirecting care is high, parent‐offspring recognition may evolve. I tested whether adult cave swallows, which nest in dense colonies and feed fledglings in mixed‐family groups, discriminate against unrelated young, using temporary chick transfers at two nestling ages and a cross‐fostering experiment. Temporary chick transfers indicated that parents bias feedings toward their own offspring near fledging (18 d) but not at about halfway through the nesting period (10 d). I also examined how parents learn to identify their offspring by cross‐fostering young 3 d after hatching and testing parental response 2 wks later. Adults did not favor their own offspring over unrelated nestlings when both were unfamiliar to the focal parents. However, when parents encountered two of their own offspring, one of which was reared by foster parents, they preferentially fed the familiar nestling. By recognizing young, cave swallow parents reduce some risks of misdirected parental investment (mobile fledglings) but not others (extra‐pair young and intraspecific brood parasitism).     

Insights into post-fledging dispersal of Bearded Vultures Gypaetus barbatus in southern Africa from GPS satellite telemetry

Capsule: Fledglings progressively increase their home range size and ranging behaviour as they age.

Aims: To examine the home range size and ranging behaviour of Bearded Vulture fledglings during the post-fledging dependence period and determine the onset of natal dispersal.

Methods: Post-fledging movements of three individuals were investigated in southern Africa using global positioning system (GPS) satellite telemetry which enabled home range sizes and distances travelled from the nest to be calculated.

Results: Fledglings increased their home range size from an average of 0.4–10 999?km² (100% Minimum Convex Polygons) and 9.13–11 466?km² (fixed 95% kernels) within the first six months post fledging. They also increased home range use as they aged with maximum daily distances travelled from the nest occurring between 98 and 136 days post fledging (when fledglings were aged between 222 and 262 days), after which time they dispersed from their natal area. Distances between fixes were highest during the dispersal period.

Conclusion: GPS satellite telemetry allows us to accurately demonstrate how fledglings progressively increase and use their home ranges as they age and undertake pre-dispersive exploratory flights. Results confirm the notion that juveniles disperse at the onset of the following breeding season and suggest that dispersal occurs earlier in the southern hemisphere.     

Movement patterns of the White-tailed Sea Eagle (Haliaeetus albicilla): post-fledging behaviour,natal dispersal onset and the role of the natal environment

Exploratory movements and natal dispersal form essential processes during early life history stages of raptors, but identifying the factors shaping individual movement decisions is challenging. Global positioning system (GPS) telemetry thereby provides a promising technique to study movement patterns on adequate spatio-temporal scales. We analysed data of juvenile White-tailed Sea Eagles Haliaeetus albicilla (WTSE) in north-east Germany (n = 24) derived from GPS tracking to extensively analyse movements between fledging and emigration from the natal territory. Our goal was to determine the time point of fledging, characterize pre-emigration movements and the onset of natal dispersal while investigating the influence of the natal environment. WTSE fledged at an average age of 72 days and showed strong excursive behaviour during the post-fledging period regarding the number, distance and duration of excursions, yet with high individual variability. Excursive behaviour did not differ between sexes. On average, WTSE left the parental territory 93 days after fledging. The quantity of excursive behaviour delayed the timing of emigration and WTSE tended to postpone their emigration when foraging water was accessible within the boundaries of their parental territory. The overall results suggest that young WTSE assess the quality of the natal environment via pre-emigration movements and stay in their territory of origin for as long as internal and external conditions allow for it. Our study is one of the first to characterize post-fledging and natal dispersal movements of young WTSE to such an extent and applies modern techniques to understand related movements in relation to the natal environment. The results emphasize the urgent necessity for the extension of currently existing nest protection periods and guaranteeing sustainable management of potential breeding and foraging grounds for WTSE. Ultimately, the results are relevant for all large raptor species sensitive to human-related disturbance, as they support the increasing importance of regulations with spatio-temporal specifications for breeding populations of large raptors in densely human-inhabited areas with increasing alteration of land.     

Testing common assumptions in studies of songbird nest success

We studied Ovenbird Seiurus aurocapilla and Golden‐winged Warbler Vermivora chrysoptera populations in northern Minnesota, USA, to test two common assumptions in studies of songbird nest success: (1) that the condition of an empty nest on or near its expected fledge date is an indicator of nest fate; and (2) that the presence of a fledgling or family group within a territory confirms a successful nest in that territory. We monitored the condition of nests and used radiotelemetry to monitor juveniles through the expected fledging date and early post‐fledging period. Of nests that contained nestlings 1–2 days before the expected fledge date, fates were misidentified using nest condition alone for 9.5% of Ovenbird nests, but those misidentifications were made in both directions (succeeded or failed), yielding only a small bias in estimated nest success. However, 20% of Golden‐winged Warbler nests were misidentified as successful using nest condition during the final visit interval, biasing the nest success estimate upward by 21–28% depending on the treatment of uncertain nest fates. Fledgling Ovenbirds from 58% of nests travelled beyond their natal territory within 24 h, rising to 98% after 5 days, and those fledglings travelled up to 390 m from nests within 10 days of fledging. Fledgling Golden‐winged Warblers from 13% of nests travelled beyond their natal territory within 24 h, rising to 85% after 5 days, and those fledglings travelled up to 510 m from nests within 10 days of fledging. We conclude that nest condition and fledgling presence can be misleading indicators of nest fate, probably commonly biasing nest success estimates upward, and we recommend that these assumptions should be tested in additional species.     

Juvenile survival and recruitment of wood thrushes Hylocichla mustelina in a forest fragment

We tested if juvenile survival and recruitment (returning to breed) of wood thrushes Hylocichla mustelina into their natal population was dependent on several measures of nestling condition, growth, and site fidelity. Overall, nestling mass, wing chord, condition, and rank within the brood did not affect the probability of survival to the post-fledging stage, independence, or recruitment. We did not identify any morphometric differences among nestlings that remained in the study area after fledging and those that did not (or those that did not survive). Time of season and the number of days nestlings were present in the study area after hatching, or site fidelity, were the only variables measured that positively influenced juvenile survival and recruitment. Based on a restricted sample, fledglings that eventually recruited did not differ in size during post-fledging or post-independence from fledglings that did not return to breed. Independent, immigrant hatching-year (HY) birds are briefly described. Overall, immigrant HY birds had a higher probability of recruitment than all local fledglings. There was no difference in the probability of recruitment between immigrant HY birds and independent local fledglings (those present ≥35 days after hatching), however. Similar to local young, the number of days present in the study area increased the likelihood of recruitment for immigrant HY birds, although these effects could not be distinguished from those of emigration or survival.     

The post‐fledging period in a tropical bird: patterns of parental care and survival

How environmental conditions affect the timing and extent of parental care is a fundamental question in comparative studies of life histories. The post‐fledging period is deemed critical for offspring fitness, yet few studies have examined this period, particularly in tropical birds. Tropical birds are predicted to have extended parental care during the post‐fledging period and this period may be key to understanding geographic variation in avian reproductive strategies. We studied a neotropical passerine, the western slaty‐antshrike Thamnophilus atrinucha, and predicted greater care and higher survival during the post‐fledging period compared to earlier stages. Furthermore, we predicted that duration of post‐fledging parental care and survival would be at the upper end of the distribution for Northern Hemisphere passerines. Correspondingly, we observed that provisioning continued for 6–12 weeks after fledging. In addition, provisioning rate was greater after fledging and offspring survival from fledging to independence was 75%, greater than all estimates from north‐temperate passerines. Intervals between nesting attempts were longer when the first brood produced successful fledglings compared to nests where offspring died either in the nest or upon fledging. Parents delayed initiating second nests after the first successful brood until fledglings were near independence. Our results indicate that parents provide greater care after fledging and this extended care likely increased offspring survival. Moreover, our findings of extended post‐fledging parental care and higher post‐fledging survival compared to Northern Hemisphere species have implications for understanding latitudinal variation in reproductive effort and parental investment strategies.     

Postfledging parental care in Savannah sparrows: sex, size and survival

We investigated postfledging parental care in a philopatric population of Savannah sparrows,Passerculus sandwichensis , breeding on Kent Island, New Brunswick, Canada in an effort to understand the factors influencing adult birds' decisions about parental investment in offspring. Brood division was not based on offspring sex: male and female parents were equally likely to care for sons or daughters. The total duration of parental care, from hatching to independence, was similar for sons and daughters (median=23 days), regardless of the sex of the care-giving parent. The duration of parental care also corresponded closely to the time required for juveniles to acquire basic foraging skills. Despite high levels of extrapair paternity, male Savannah sparrows invested as much in postfledging care and were as effective as females in caring for fledglings, based on recruitment of fledglings into the breeding population the following year. Male parents were more likely to care for smaller fledglings and for offspring from early broods (presumably to enable females to dedicate their efforts towards second clutches). Caring for fledglings was costly for parents: survivorship decreased as a function of the duration of postfledging parental care and the number of fledglings cared for. Parental survivorship, however, was not affected by the sex of the fledglings cared for. This study suggests that sex-biased provisioning may be unlikely except in species with strongly sexually dimorphic offspring, biased offspring sex ratios and sex-biased natal dispersal. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Do fledgling and pre‐breeding Common Swifts Apus apus take part in aerial roosting? An answer from a radiotracking experiment

This study has shown that fledgling Common Swifts Apus apus spend the first post-fledging night of their life on the wing and that pre-breeders also spend the full night on the wing. Even though this work was conducted during an unusually cold, wet period, the results show that fledglings do not return to their natal colony in the week after fledging. It also demonstrates that yearlings are only slightly more likely than fledglings to spend any time at a particular colony, but are more likely to move from colony to colony. Older pre-breeders are more likely to spend more time at and revisit a particular colony more often than yearlings. It is our observation that only right at the end of the breeding duties will the parents participate in an evening ascent, and even then many of them return to their nest for the evening. Breeding adults displayed the greatest devotion to a particular colony. But even among such adults we detected some that ceased caring for their young a few days prior to their fledging. Adults roost in their nestbox if they meet with bad weather.     

Detrimental impacts of radiotransmitters on juvenile Louisiana Waterthrushes

ABSTRACT.   The Louisiana Waterthrush (waterthrush; Seiurus motacilla ) is a forest-dwelling, Nearctic-Neotropical migratory passerine that nests along streams. We attached radiotransmitters (0.6–0.8 g) to 12 nestling waterthrushes using snug, elastic loops. At three nests, adult waterthrushes were videotaped removing radio-tagged young from the nest. In addition, we recovered nine radio-backpacks (with two still attached to the carcasses of nestlings) near nests within a few days after attaching transmitters. Only one of 12 radio-tagged young was relocated more than 24 h after attaching the transmitter. Thus, the method of transmitter attachment we used was not effective. Using snug, nonelastic loops (e.g., nylon) for the harness may reduce the loss of transmitters, but may injure the skin as fledglings grow. Other possible alternatives include (1) gluing the transmitter to skin on the back of nestlings, (2) capturing fledglings in mist nets and attaching transmitters a week or more after fledging by which time contour feathers have grown and the likelihood of a parent removing the transmitter may be reduced, or (3) attempting to monitor fledglings without attaching transmitters. The success of the latter two alternatives would likely be enhanced by attaching transmitters to adults and then tracking them to locate their still-dependent fledglings.     

Females compensate for moult‐associated male nest desertion in Hooded Warblers

Uniparental offspring desertion occurs in a wide variety of avian taxa and usually reflects sexual conflict over parental care. In many species, desertion yields immediate reproductive benefits for deserters if they can re‐mate and breed again during the same nesting season; in such cases desertion may be selectively advantageous even if it significantly reduces the fitness of the current brood. However, in many other species, parents desert late‐season offspring when opportunities to re‐nest are absent. In these cases, any reproductive benefits of desertion are delayed, and desertion is unlikely to be advantageous unless the deserted parent can compensate for the loss of its partner and minimize costs to the current brood. We tested this parental compensation hypothesis in Hooded Warblers Setophaga citrina, a species in which males regularly desert late‐season nestlings and fledglings during moult. Females from deserted nests effectively doubled their provisioning efforts, and nestlings from deserted nests received just as much food, gained mass at the same rate, and were no more likely to die from either complete nest predation or brood reduction as young from biparental nests. The female provisioning response, however, was significantly related to nestling age; females undercompensated for male desertion when the nestlings were young, but overcompensated as nestlings approached fledging age, probably because of time constraints that brooding imposed on females with young nestlings. Overall, our results indicate that female Hooded Warblers completely compensate for male moult‐associated nest desertion, and that deserting males pay no reproductive cost for desertion, at least up to the point of fledging. Along with other studies, our findings support the general conclusion that late‐season offspring desertion is likely to evolve only when parental compensation by the deserted partner can minimize costs to the current brood.     

Neuronal recruitment in adult zebra finch brain during a reproductive cycle

Previous studies suggest that adult neurogenesis and neuronal replacement are related to the acquisition of new information. The present study supports this hypothesis by showing that there is an increase in new neuron recruitment in brains of adult male and female zebra finches that coincides with the need to memorize vocalizations of nestlings before they fledge. We counted [(3)H]-Thymidine labeled neurons 40 days after [(3)H]-Thymidine injections. These counts were made in the parents' brains at the time eggs hatched, at the time juveniles fledged and still needed parental care, and at the time juveniles were already independent. We focused on nidopallium caudale (NC), a brain region which plays a role in sound processing. Recruitment of new NC neurons increased at the time the young fledged, followed by a significant decrease when the young reached independence. We suggest that this increase enables parents to recognize their own young when they are still dependent on parental feeding, yet easily lost among other fledglings in the colony. We saw no such increase in neuronal recruitment in the olfactory bulb, suggesting anatomical specificity for the effect seen in NC. We also found a preliminary, positive correlation between number of fledglings and number of new NC neurons in the parents' brain at fledging, suggesting that the number of neurons recruited is sensitive to the number of young fledged.     

Survivorship, dispersal and sex ratios of Zebra Finches Taeniopygia guttata in southeast Australia

Membership of three permanent breeding colonies of Zebra Finches Taeniopygia guttata studied in farmland changed continually due to arrival and departure of birds from distant colonies. Sixty-six percent of adults stayed for less than 1 month, and many that stayed longer disappeared for extended periods. Over 78% of adults captured were hatched in other colonies and only 23% made a breeding attempt in their natal colony. There was no sex-biased natal dispersal or philopatry, but there were sex differences in the timing of dispersal. Sex ratios at the end of parental care were variable and may depend on food resources. Adult ratios were slightly male-biased. Annual losses of adults ranged from 72 to 82% across colonies, but mortalities and dispersal were heavily confounded by high adult mobility. The oldest bird was more than 5 years old. A total of 67% of young were lost between fledging and nutritional independence at 35 days of age, and only 20% of fledglings survived to day 80, the age of first breeding. Artificial supplies of seed at baited walk-in traps prolonged the stay of dispersing adults from other colonies, enhanced the survivorship of young hatched in the colony and possibly affected the secondary sex ratio. In this southeast part of their Australia-wide distribution, Zebra Finch populations appear to be highly mobile over a very large home range with extensive free interchange of members among a number of permanent breeding colonies. High mobility may be adaptive for exploiting patches of seed and water in a highly erratic environment.     

Great Spotted Cuckoo Fledglings Often Receive Feedings from Other Magpie Adults than Their Foster Parents: Which Magpies Accept to Feed Foreign Cuckoo Fledglings?

Natural selection penalizes individuals that provide costly parental care to non-relatives. However, feedings to brood-parasitic fledglings by individuals other than their foster parents, although anecdotic, have been commonly observed, also in the great spotted cuckoo (Clamator glandarius) – magpie (Pica pica) system, but this behaviour has never been studied in depth. In a first experiment, we here show that great spotted cuckoo fledglings that were translocated to a distant territory managed to survive. This implies that obtaining food from foreign magpies is a frequent and efficient strategy used by great spotted cuckoo fledglings. A second experiment, in which we presented a stuffed-cuckoo fledgling in magpie territories, showed that adult magpies caring for magpie fledglings responded aggressively in most of the trials and never tried to feed the stuffed cuckoo, whereas magpies that were caring for cuckoo fledglings reacted rarely with aggressive behavior and were sometimes disposed to feed the stuffed cuckoo. In a third experiment we observed feedings to post-fledgling cuckoos by marked adult magpies belonging to four different possibilities with respect to breeding status (i.e. composition of the brood: only cuckoos, only magpies, mixed, or failed breeding attempt). All non-parental feeding events to cuckoos were provided by magpies that were caring only for cuckoo fledglings. These results strongly support the conclusion that cuckoo fledglings that abandon their foster parents get fed by other adult magpies that are currently caring for other cuckoo fledglings. These findings are crucial to understand the co-evolutionary arms race between brood parasites and their hosts because they show that the presence of the host''s own nestlings for comparison is likely a key clue to favour the evolution of fledgling discrimination and provide new insights on several relevant points such as learning mechanisms and multiparasitism.     

Nestling aggression in broods of a siblicidal kingfisher, the laughing kookaburra

Third-hatched nestling in broods of the laughing kookaburra(Dacelo novaeguineae) are often killed by aggressive attacksfrom their older siblings within days of hatching. By installingsurveillance cameras inside nest hollows, we examined nestlingaggression over the "siblicidal" period, in particular to identifywhether parental behavior and competitive disparities betweennestlings affected aggression, and hence the likelihood ofsiblicide. Aggression decreased as nestlings aged and dominancehierarchies became established. The first-hatched nestling was the most aggressive. Fighting between the first-hatched nestlingand its closest rival (second-hatched nestling) increased whenthe hatch interval between them was short, when the size differencebetween them at hatching was small, and when the second nestlingwas female. Female nestlings are faster-growing than males,so young sisters may be an incipient threat requiring preemptiveaction by older siblings. When the second-hatched nestlingwas female, the first-hatched also attacked the third-hatched nestling more frequently. Thus the third-hatched nestling seemsto experience some of the "overflow" of aggression occurringbetween its two older siblings. Nestlings in siblicidal broodswere not fed less compared to nonsiblicidal broods; this isunsurprising because siblicide occurs when feeding rates arecomparatively low. However, siblicidal nestlings were broodedless, and in shorter bouts, which allowed them more time tofight.     

Behaviour and parental care of Skylark Alauda arvensis chicks

I studied parental care and fledgling dispersion of Skylarks Alauda arvensis during the last 4 days of the nestling period and the first 4 days after the nestlings left the nest but before they were able to fly. The study compared parental care in three different crop types: spring barley, grass and set-aside. Both parents made more provisioning trips and delivered more food to fledglings than to nestlings. Fledglings received fewer items per trip than did nestlings. Feeding distances did not differ between nestling and post-Hedging periods for any crop type. This suggests that fledging was associated with a change in parental foraging strategies. Parental care differed between broods from different crop types. During the last 4 days of the nestling period, the feeding frequencies were 3.4 trips per young per hour in spring barley fields, 5.8 in grass and 7.3 in set-aside. The mean distances to the feeding area were 233 m in spring barley fields, 155 m in grass and 120 m in set-aside. The load size of provisioning trips was significantly higher in set-aside than in spring barley and grass. During the first 4 days after fledging, the feeding frequencies were 2.2 successful trips per young per hour in spring barley fields, 4.1 in grass and 5.1 in set-aside. The feeding distances were 210 m in spring barley fields, 162 m in grass and 120 m in set-aside. Load size of provisioning trips was significantly higher in set-aside than in spring barley and grass. The mean dispersion of fledglings was significantly greater in fields of spring barley compared with grass fields and set-aside.     

Post-fledging brood and care division in the roseate tern (Sterna dougallii)

Extended post-fledging parental care is an important aspect of parental care in birds, although little studied due to logistic difficulties. Commonly, the brood is split physically (brood division) and/or preferential care is given to a subset of the brood by one parent or the other (care division). Among gulls and tern (Laridae), males and females generally share parental activities during the pre-fledging period, but the allocation of parental care after fledging is little documented. This study examined the behaviour of male and female roseate terns (Sterna dougallii) during the late chick-rearing and early post-fledging periods, and in particular the amount of feeds and the time spent in attendance given to individual chicks/fledglings. Pre-fledging parental care was biparental in all cases. Post-fledging parental care was dependent on the number of fledglings in the brood. Males and females continued biparental care in clutches with one surviving fledgling, while in two-fledgling clutches, males fed the A-fledgling while females fed the B-fledgling. Overall, there was no difference in attendance, only in feeds. This division of care may be influenced by the male only being certain of the paternity of the A-chick but not by chick sex.     

Population sex ratio shift from fledging to recruitment: consequences for demography in a philopatric seabird

In many dimorphic bird species, offspring sex ratio is skewed towards the production of the smaller sex. Offspring sex ratio can be biased in monomorphic birds however, and the demographic consequences of such bias are unknown. Sex-specific mortality and dispersal are fundamental mechanisms of sex ratio adjustment at the population level, but evidence for adjustments is weak and feedback into population dynamics poorly understood. Here, we link sex ratio at fledging with sex-specific subadult return and recruitment at the Banter See common tern Sterna hirundo colony. Using molecular sexing methods and a remote detection system, we permanently tracked individuals from four complete cohorts (n=1171 fledglings) across these life-history stages at their natal colony site, which permitted a structured analysis of sex ratio across multiple seasons. Sex ratio shifted significantly from significant daughter dominance at fledging to higher proportions of natal males among recruits; return and recruitment rates of sons were significantly higher than daughters (p≤0.002). No significant between-year differences were detected. 47.4% of natal male recruits were paired with a non-natal female, but only 37.0% of natal female recruits had a non-natal partner. Elasticity analysis suggested that natal males have a greater influence on natal population growth rate than natal females. Sex biased dispersal is the most probable reason for these results indicating higher emigration to and immigration from other colonies in females, the less territorial and less philopatric sex. This pattern may be related to different gender roles in parental duties and with respect to competition for local resources.